Annalisa Franco - Profile on Academia.edu (original) (raw)
Papers by Annalisa Franco
International Journal of Solids and Structures, 2016
The contact stresses in a bonded joint due to differential thermal expansions are calculated by c... more The contact stresses in a bonded joint due to differential thermal expansions are calculated by considering the adhesive as an elastic rectangle confined by plates representing the adherends. The interface is cohesive in type, so that the contact area is a perfectly adherent region surrounded by cohesive areas where slip occurs at constant shear-stress. The problem is formulated in terms of Papkovich-Fadle eigenfunctions, which satisfy the boundary conditions on the stress free edges. The resulting integral equations are solved with the Jacobi integration formula. The size of the cohesive zone, which is determined by imposing the finiteness of the contact stresses at the frontier with the bonded region, depends upon the length and height of the joint. In very long joints the result tends to the technical rule of thumb traditionally employed to design such joints, but for intermediate lengths the elastic solution is quite different.
From design by testing to structural verification of glass: the role of subcritical crack propagation
There are in general two main issues associated with the “structural” use of glass. On the one ha... more There are in general two main issues associated with the “structural” use of glass. On the one hand, analytical verifications have to be made to meet the load bearing capacity requirements based upon structural models. On the other hand, a common practice is to test a few full-scale prototypes and verify that they break at a stress level higher than the design strength. However, the strength of the structural element strongly depends upon several aspects associated with the opening of cracks on the material surface. Surface defectiveness, specimen size, subcritical crack speed, load history and type of stress, may all strongly influence the material gross response. Starting from a consolidated model of subcritical crack propagation and a distribution à la Weibull of defects, an analytical approach to these problems is now proposed. Safety domains are calculated and new verification formulae for the combination of variable actions are presented. The probability of glass failure for a...
Passive Control of Steel Storage Racks for Parmigiano Reggiano Cheese under Seismic Accelerations
Journal of Earthquake Engineering, 2015
ABSTRACT
International Journal of Non-Linear Mechanics, 2014
The problem of an elastic bar bonded to an elastic half space and pulled at one end is considered... more The problem of an elastic bar bonded to an elastic half space and pulled at one end is considered to model the performance of FRP strips glued to concrete or masonry substrates. If the bond is perfect, stress singularities at both bar-extremities do appear. These can be removed by assuming cohesive contact forces à là Baranblatt that annihilate the stress intensity factor. We show that the presence of such cohesive zones is crucial to predict the experimentally measured Effective Bond Length (EBL), i.e., the bond length beyond which no apparent increase of strength is attained. In particular, it is the cohesive zone at the loaded end of the stiffener, rather than that at the free end, that governs the phenomenon because the EBL coincides with the maximal length of such zone. The proposed approach provides better estimates than formulas proposed in technical standards.
Fiber Reinforced Polymers (FRP) are commonly used for strengthening and rehabilitation of concret... more Fiber Reinforced Polymers (FRP) are commonly used for strengthening and rehabilitation of concrete or masonry structures, by gluing strips or plates made of this material on the surface of the weak material. Experimental studies have provided evidence that the main failure mode is the debonding of the FRP stiffener from the support, triggered by high stress concentrations at the extremities of the stiffener. Fracture propagates firstly parallel to the interface and then in the substrate, until complete separation between the two adherents occurs. Final failure is often characterized by the detachment of a wedge-shaped portion of the substrate, which remains bonded to the FRP strip. In order to describe the whole process, the model problem considered here is that of a finite thin elastic stiffener, bonded to an elastic half-space in generalized plane stress, pulled at one end by an axial force. The thickness of the stiffener is supposed very small, so that its bending stiffness can b...
Applied Sciences, 2021
Recycled materials from construction and demolition waste, such as recycled concrete aggregate, r... more Recycled materials from construction and demolition waste, such as recycled concrete aggregate, recycled brick aggregate, or recycled asphalt coming from the milling of road/motorway surfaces, are the key for a sustainable production of concrete. This paper reviews in particular the use of recycled asphalt pavement (RAP) aggregates in the production of concrete for structural uses. An overview is initially presented to describe the different areas of use of RAP, its definition and the limitations imposed by codes and standards. Relatively to the experimental data provided by the literature, a comparison with the Italian minimum requirements is also provided. Lastly, the influence of RAP on the characteristics of concrete such as compressive strength, flexural strength, Young’s Modulus and a study of durability are presented to define the possible applications of RAP in structural concrete in relation to the current allowable percentage of substitution.
Engineering Structures, 2015
Verification formulae for structural glass under combined variable loads
Engineering Structures, 2015
ABSTRACT It is well known that, depending upon the thermo-hygrometric environment, surface flaws ... more ABSTRACT It is well known that, depending upon the thermo-hygrometric environment, surface flaws in glass can grow over time even when they are well below the critical size, eventually leading to failure of the stressed material. This phenomenon, usually referred to as subcritical crack growth, or static fatigue, implies that the macroscopic strength of glass depends upon the characteristic duration of the applied loads. Various criteria have been proposed to evaluate the effects of the simultaneous combinations of actions applied at different times of the load history. Here, starting from a consolidated model of subcritical crack growth, an analytical approach to this problem is presented. Safety domains are calculated and compared with the approaches prescribed by recent proposals for standards. The analysis of a few case studies confirms that some approaches are not on the safe side, whereas other approaches can be too conservative. A proposal for new verification formulae is presented.
International Journal of Solids and Structures, 2013
An effective way to strengthen deteriorated concrete or masonry structures is to glue to them, at... more An effective way to strengthen deteriorated concrete or masonry structures is to glue to them, at critical regions, strips or plates made of Fiber Reinforced Polymers (FRP). The reliability of this technique depends upon interfacial adhesion, whose performance is usually evaluated through an energetic balance, assuming that the support is rigid. The present study analyzes the contact problem between reinforcement and substrate, both assumed to be linear elastic. The solution of the resulting integral equations is expressed in terms of Chebyshev polynomials. A generalization to this problem of the Crack Closure Integral Method developed by Irwin allows to calculate the energy release rate associated with the debonding of the stiffener. Energetic balance à la Griffith emphasizes the role played by the length of the stiffener and the deformation of the substrate, predicting load vs. displacement curves that, in agreement with experimental measurements, exhibit a snap-back phase.
The problem of an elastic bar bonded to an elastic half space and pulled at one end is considered... more The problem of an elastic bar bonded to an elastic half space and pulled at one end is considered to model the performance of FRP strips glued to concrete or masonry substrates. If the bond is perfect, stress singularities at both bar-extremities do appear. These can be removed by assuming cohesive contact forces à là Baranblatt that annihilate the stress intensity factor. We show that the presence of such cohesive zones is crucial to predict the experimentally measured effective bond length (EBL), i.e., the bond length beyond which no apparent increase of strength is attained. In particular, it is the cohesive zone at the loaded end of the stiffener, rather than that at the free end, that governs the phenomenon because the EBL coincides with the maximal length of such a zone. The proposed approach provides better estimates than formulas proposed in technical standards.
Composite Structures, 2014
To strengthen concrete or masonry, a modern technique uses adherent strips made of Fiber Reinforc... more To strengthen concrete or masonry, a modern technique uses adherent strips made of Fiber Reinforced Polymer (FRP). A model problem for this is here considered, represented by an elastic stiffener pulled at one end, in adhesive contact with an elastic half space in generalized plane stress. An analytical solution is developed under the hypothesis à la Baranblatt that cohesive adhesion forces remain active between the two materials when relative slip occurs (provided this is less than a critical value), so that the stress singularity predicted by the theory of elasticity in the case of perfect bonding is removed. We find that the bond length beyond which no further increase of strength could be achieved, referred to as the effective bond length, coincides in practice with the ultimate length of the cohesive zone, i.e., its maximal extension prior that the critical slip limit is attained. The debonding process in a pull-out experiment is analyzed in detail. Results are in better agreement with experimental data than those obtainable with traditional models, which neglect as a rule the deformation of the substrate.
International Journal of Solids and Structures, 2014
Fiber-Reinforced-Polymer (FRP) strips can be glued to the surface of concrete or masonry structur... more Fiber-Reinforced-Polymer (FRP) strips can be glued to the surface of concrete or masonry structures to improve their strength. Pull-out tests on FRP bonds have shown a progressive failure of the adhesive joint involving early-stage cracking parallel to the axis of the FRP stiffener, and an inclined crack initiating at the free end of the stiffener and extending into the quasi-brittle substrate in the latest stage. The subsurface crack produces a characteristic wedge-shaped spall. There is no consensus on the reasons for the transition from cracking along the bond to cracking within the substrate. Therefore a Linear Elastic Fracture Mechanics model problem is presented here that accounts for and provides improved understanding of the formation of the subsurface crack. The boundary value problem is solved analytically using the distributed dislocation technique. Competition between crack extension along the adhesive joint and into the substrate is quantified using a quantized crack propagation criterion, whereby the crack does not advance in infinitesimal continuous increments, but instead in finite steps of length comparable to the characteristic dimensions of the material microstructure. The model predicts results that are in good agreement with experimental evidence.
International Journal of Solids and Structures, 2016
The contact stresses in a bonded joint due to differential thermal expansions are calculated by c... more The contact stresses in a bonded joint due to differential thermal expansions are calculated by considering the adhesive as an elastic rectangle confined by plates representing the adherends. The interface is cohesive in type, so that the contact area is a perfectly adherent region surrounded by cohesive areas where slip occurs at constant shear-stress. The problem is formulated in terms of Papkovich-Fadle eigenfunctions, which satisfy the boundary conditions on the stress free edges. The resulting integral equations are solved with the Jacobi integration formula. The size of the cohesive zone, which is determined by imposing the finiteness of the contact stresses at the frontier with the bonded region, depends upon the length and height of the joint. In very long joints the result tends to the technical rule of thumb traditionally employed to design such joints, but for intermediate lengths the elastic solution is quite different.
From design by testing to structural verification of glass: the role of subcritical crack propagation
There are in general two main issues associated with the “structural” use of glass. On the one ha... more There are in general two main issues associated with the “structural” use of glass. On the one hand, analytical verifications have to be made to meet the load bearing capacity requirements based upon structural models. On the other hand, a common practice is to test a few full-scale prototypes and verify that they break at a stress level higher than the design strength. However, the strength of the structural element strongly depends upon several aspects associated with the opening of cracks on the material surface. Surface defectiveness, specimen size, subcritical crack speed, load history and type of stress, may all strongly influence the material gross response. Starting from a consolidated model of subcritical crack propagation and a distribution à la Weibull of defects, an analytical approach to these problems is now proposed. Safety domains are calculated and new verification formulae for the combination of variable actions are presented. The probability of glass failure for a...
Passive Control of Steel Storage Racks for Parmigiano Reggiano Cheese under Seismic Accelerations
Journal of Earthquake Engineering, 2015
ABSTRACT
International Journal of Non-Linear Mechanics, 2014
The problem of an elastic bar bonded to an elastic half space and pulled at one end is considered... more The problem of an elastic bar bonded to an elastic half space and pulled at one end is considered to model the performance of FRP strips glued to concrete or masonry substrates. If the bond is perfect, stress singularities at both bar-extremities do appear. These can be removed by assuming cohesive contact forces à là Baranblatt that annihilate the stress intensity factor. We show that the presence of such cohesive zones is crucial to predict the experimentally measured Effective Bond Length (EBL), i.e., the bond length beyond which no apparent increase of strength is attained. In particular, it is the cohesive zone at the loaded end of the stiffener, rather than that at the free end, that governs the phenomenon because the EBL coincides with the maximal length of such zone. The proposed approach provides better estimates than formulas proposed in technical standards.
Fiber Reinforced Polymers (FRP) are commonly used for strengthening and rehabilitation of concret... more Fiber Reinforced Polymers (FRP) are commonly used for strengthening and rehabilitation of concrete or masonry structures, by gluing strips or plates made of this material on the surface of the weak material. Experimental studies have provided evidence that the main failure mode is the debonding of the FRP stiffener from the support, triggered by high stress concentrations at the extremities of the stiffener. Fracture propagates firstly parallel to the interface and then in the substrate, until complete separation between the two adherents occurs. Final failure is often characterized by the detachment of a wedge-shaped portion of the substrate, which remains bonded to the FRP strip. In order to describe the whole process, the model problem considered here is that of a finite thin elastic stiffener, bonded to an elastic half-space in generalized plane stress, pulled at one end by an axial force. The thickness of the stiffener is supposed very small, so that its bending stiffness can b...
Applied Sciences, 2021
Recycled materials from construction and demolition waste, such as recycled concrete aggregate, r... more Recycled materials from construction and demolition waste, such as recycled concrete aggregate, recycled brick aggregate, or recycled asphalt coming from the milling of road/motorway surfaces, are the key for a sustainable production of concrete. This paper reviews in particular the use of recycled asphalt pavement (RAP) aggregates in the production of concrete for structural uses. An overview is initially presented to describe the different areas of use of RAP, its definition and the limitations imposed by codes and standards. Relatively to the experimental data provided by the literature, a comparison with the Italian minimum requirements is also provided. Lastly, the influence of RAP on the characteristics of concrete such as compressive strength, flexural strength, Young’s Modulus and a study of durability are presented to define the possible applications of RAP in structural concrete in relation to the current allowable percentage of substitution.
Engineering Structures, 2015
Verification formulae for structural glass under combined variable loads
Engineering Structures, 2015
ABSTRACT It is well known that, depending upon the thermo-hygrometric environment, surface flaws ... more ABSTRACT It is well known that, depending upon the thermo-hygrometric environment, surface flaws in glass can grow over time even when they are well below the critical size, eventually leading to failure of the stressed material. This phenomenon, usually referred to as subcritical crack growth, or static fatigue, implies that the macroscopic strength of glass depends upon the characteristic duration of the applied loads. Various criteria have been proposed to evaluate the effects of the simultaneous combinations of actions applied at different times of the load history. Here, starting from a consolidated model of subcritical crack growth, an analytical approach to this problem is presented. Safety domains are calculated and compared with the approaches prescribed by recent proposals for standards. The analysis of a few case studies confirms that some approaches are not on the safe side, whereas other approaches can be too conservative. A proposal for new verification formulae is presented.
International Journal of Solids and Structures, 2013
An effective way to strengthen deteriorated concrete or masonry structures is to glue to them, at... more An effective way to strengthen deteriorated concrete or masonry structures is to glue to them, at critical regions, strips or plates made of Fiber Reinforced Polymers (FRP). The reliability of this technique depends upon interfacial adhesion, whose performance is usually evaluated through an energetic balance, assuming that the support is rigid. The present study analyzes the contact problem between reinforcement and substrate, both assumed to be linear elastic. The solution of the resulting integral equations is expressed in terms of Chebyshev polynomials. A generalization to this problem of the Crack Closure Integral Method developed by Irwin allows to calculate the energy release rate associated with the debonding of the stiffener. Energetic balance à la Griffith emphasizes the role played by the length of the stiffener and the deformation of the substrate, predicting load vs. displacement curves that, in agreement with experimental measurements, exhibit a snap-back phase.
The problem of an elastic bar bonded to an elastic half space and pulled at one end is considered... more The problem of an elastic bar bonded to an elastic half space and pulled at one end is considered to model the performance of FRP strips glued to concrete or masonry substrates. If the bond is perfect, stress singularities at both bar-extremities do appear. These can be removed by assuming cohesive contact forces à là Baranblatt that annihilate the stress intensity factor. We show that the presence of such cohesive zones is crucial to predict the experimentally measured effective bond length (EBL), i.e., the bond length beyond which no apparent increase of strength is attained. In particular, it is the cohesive zone at the loaded end of the stiffener, rather than that at the free end, that governs the phenomenon because the EBL coincides with the maximal length of such a zone. The proposed approach provides better estimates than formulas proposed in technical standards.
Composite Structures, 2014
To strengthen concrete or masonry, a modern technique uses adherent strips made of Fiber Reinforc... more To strengthen concrete or masonry, a modern technique uses adherent strips made of Fiber Reinforced Polymer (FRP). A model problem for this is here considered, represented by an elastic stiffener pulled at one end, in adhesive contact with an elastic half space in generalized plane stress. An analytical solution is developed under the hypothesis à la Baranblatt that cohesive adhesion forces remain active between the two materials when relative slip occurs (provided this is less than a critical value), so that the stress singularity predicted by the theory of elasticity in the case of perfect bonding is removed. We find that the bond length beyond which no further increase of strength could be achieved, referred to as the effective bond length, coincides in practice with the ultimate length of the cohesive zone, i.e., its maximal extension prior that the critical slip limit is attained. The debonding process in a pull-out experiment is analyzed in detail. Results are in better agreement with experimental data than those obtainable with traditional models, which neglect as a rule the deformation of the substrate.
International Journal of Solids and Structures, 2014
Fiber-Reinforced-Polymer (FRP) strips can be glued to the surface of concrete or masonry structur... more Fiber-Reinforced-Polymer (FRP) strips can be glued to the surface of concrete or masonry structures to improve their strength. Pull-out tests on FRP bonds have shown a progressive failure of the adhesive joint involving early-stage cracking parallel to the axis of the FRP stiffener, and an inclined crack initiating at the free end of the stiffener and extending into the quasi-brittle substrate in the latest stage. The subsurface crack produces a characteristic wedge-shaped spall. There is no consensus on the reasons for the transition from cracking along the bond to cracking within the substrate. Therefore a Linear Elastic Fracture Mechanics model problem is presented here that accounts for and provides improved understanding of the formation of the subsurface crack. The boundary value problem is solved analytically using the distributed dislocation technique. Competition between crack extension along the adhesive joint and into the substrate is quantified using a quantized crack propagation criterion, whereby the crack does not advance in infinitesimal continuous increments, but instead in finite steps of length comparable to the characteristic dimensions of the material microstructure. The model predicts results that are in good agreement with experimental evidence.